1. Field of the Invention
The present disclosure relates to an electrostatic charge image developing toner, electrostatic charge image developer, and image forming apparatus that are used in an electrophotographic system.
2. Description of the Related Art
In a copy machine, printer, digital multi-functional peripheral and other image forming apparatuses for forming images on sheets of paper using an electrophotographic system, electrostatic charge images (electrostatic latent images) are formed on circumferential surfaces of photoreceptor drums serving as image carriers, and these electrostatic charge images are developed into toner images by a developing device using a toner. The toner images on the photoreceptor drums are transferred onto a sheet by a transfer device, and then heated and pressurized by a fixing device, in order to be fixed on the sheet. The sheet having the toner images fixed thereon is eventually discharged to the outside of the image forming apparatus.
With a view to reducing the effects on the environment and running costs, those units that are used in an electrophotographic process are designed to have long lives. Above all, the photoreceptor drums, playing a key role in forming images, have been required for keeping the stable conditions thereof for a long period of time.
In order to withstand long-term use, amorphous silicon photoreceptors have been used as the photoreceptor drums due to their wear resistance of surfaces thereof.
Furthermore, an image forming apparatus, in which the amorphous silicon photoreceptors are used, uses a toner that contains fine particles containing a predetermined percentage of zinc oxide and metallic elements other than zinc elements, for the purpose of providing the toner with fluidity and enhancing the cleaning characteristics of the toner.
However, because the amorphous silicon photoreceptors exhibit wear resistance, the surfaces of these photoreceptors need to be so designed that they are polished, by adding an abrasive compound or the like to the toner so that the surfaces are not contaminated by discharge products that are generated from charging rollers and the like during a charging process. The technology described above, however, does not take such a problem into consideration sufficiently.
In addition, in order to keep the photoreceptor drums in good condition for a long period of time, it is important to prevent the generation of pinholes on the photoreceptor drums, which are caused by separation discharge when a non-transferred toner is recovered by a cleaning blade. When there is no sufficiently low-resistance external additive layer around an edge of the cleaning blade, the pinholes are caused as electric charges accumulate in the toner entering an edge area between the cleaning blade and the photoreceptor drum, and, consequently photoreceptor layers are damaged by the discharge that is caused when voltage generated by the accumulated electric charges in the toner exceeds withstanding voltage of the photoreceptor layers. The pinholes are easily caused when a large amount of toner is recovered at once. Since the parts on the photoreceptor drum with pinholes are not charged, unwanted colored spots are generated on an image formed on a sheet.